› Forums › Network Management › ZeroShell › Linux QOS is not efficient enough for VoIP over shared WANs › Re: Linux QOS
I dont agree with you assumptions on QOS.
Cisco does implement LFI (Link fragmentation) but only on sync serial data lines running PPP (MLPPP) and it is only needed on line under 768kbit/sec.
Having 12ms jitter should not be a problem, as Voip channels implement jitter buffers.
Maximum one way delay for Voip is 150msec.
The problem is with ADSL, as you have a highspeed (e.g. 100Mbit/sec) ether net link to the ADSL modem there is no queue on the linux box, and thus no way to apply QOS, one way around this is to limit the outgoing speed on the Linux port to be lower than the ADSL speed and force the queue to build on the linux box where you can apply QOS rules, and ensure that the Queue on the ADSL modem is always empty.
This is for out going, for incoming you have no control. One way to reduce this impact is to throttle incoming connection to try and limit buildup of queue on incoming line, but this can never be fully achieved.